This invention relates generally to the field of respiratory gases, and in particular, to the management of respiratory gases. More specifically, the invention relates to the use of positive expiratory pressures, or PEP.
Medical research has shown that PEP improves gas exchange in the lungs under certain conditions. To create a PEP within a patient, a variety of PEP valves have been constructed to prevent respiratory gases from exiting the lungs. For example, some compressible bags, such as an AMBU bag, commercially available from AMBU International, Denmark, incorporate a PEP valve. This type of compressible bag is coupled to a facial mask that is placed over a patient""s mouth and nose. The compressible bag is compressed to deliver air to the patient""s lungs. When the patient exhales, the PEP valve creates a PEP within the patient.
One specific application of PEP is in connection with cardiopulmonary resuscitation (CPR) procedures. For example, U.S. Pat. Nos. 5,551,420 and 5,692,498, the disclosures of which are herein incorporated by reference, describe various PEP valves that may be used in connection with CPR procedures.
CPR procedures typically involve a compression phase where the patient""s chest is actively compressed, and a decompression phase where the patient""s chest is allowed to return to its decompressed state, either by its own resilience or through techniques employed to actively lift the chest. Recently, a number of devices have been developed to enhance venous blood return during the decompression phase of CPR. These devices augment venous return by either decreasing intrathoracic pressure during the decompression phase, thereby drawing venous blood into the thorax, or by pushing venous blood into the thorax by actively compressing the abdominal cavity. The use of PEP during CPR has been suggested as one way to force this blood out of the thorax. For instance, as recited in U.S. Pat. No. 5,692,498, use of a xe2x80x9cpressure-responsive expiration valve during decompression may further increase intrathoracic pressure and thereby force more blood out of the thorax.xe2x80x9d
Hence, this invention relates generally to various techniques involving the use of PEP. The invention also relates to various types of valves used to produce PEP in a patient. In one specific aspect, the invention relates to the use of PEP when performing CPR procedures.
In one embodiment of the invention, a method is provided for altering a person""s breathing. According to the method, an exit valve is interfaced with the person""s airway. The exit valve is configured such that respiratory gases are prevented from exiting the person""s lungs when the exit valve is closed. Respiratory gases are permitted to exit the person""s lungs when the exit valve is opened. Further, the exit valve is configured to open when a valve actuating pressure is met or exceeded. In use, the valve actuating pressure is varied over time. In this way, a positive expiratory pressure (PEP) is provided within the person. Further, the PEP is varied over time as the valve actuating pressure is varied. For example, the valve actuating pressure may be increased over time so that the pressure of the respiratory gases held within the patient is also increased over time.
In one particular aspect, the method is used in connection with a cardiopulmonary resuscitation (CPR) procedure where the patient""s chest is periodically compressed while the exit valve is interfaced with the person""s airway. In this way, as the patient""s chest is compressed, respiratory gases are forced against the exit valve. When the pressure of the respiratory gases meets or exceeds the actuating pressure, the valve is opened to allow the respiratory gases to exit the patient""s lungs. Optionally, the person""s chest may be compressed with a compression mechanism.
When used in association with a CPR procedure, the valve actuating pressure may be varied within a range from about 0 cm H2O to about 20 cm H2O, and more preferably in the range from about 2.5 cm H2O to about 10 cm H2O. Further, the valve actuating pressure may be varied over a time period in the range from about 5 minutes to about 30 minutes. In the event that cardiac function is successfully obtained, the exit valve may be removed from the patient""s airway.
In another particular aspect, the person""s chest may be actively lifted in an alternating manner with chest compression. In an alternative aspect, the patient""s abdomen may be periodically compressed in an alternating manner with chest compressions. By actively lifting the person""s chest or compressing the person""s abdomen, more venous blood is forced into the thorax. In still another alternative aspect, an impedance valve may be interfaced with the patient""s airway. The impedance valve may be configured to open to permit respiratory gases to flow to the person""s lungs once a threshold negative intrathoracic pressure is met or exceeded. Such an impedance valve may be employed to create a greater vacuum effect during the decompression phase of CPR to increase coronary perfusion pressure and myocardial blood flow. Use of the exit valve in combination with the impedance valve and/or techniques where the person""s chest is actively lifted or the person""s abdomen is compressed improves oxygenation while maintaining and/or increasing coronary perfusion pressure, thereby increasing the efficiency of the CPR procedure. Conveniently, the impedance valve and the exit valve may be combined into a single device.
In another embodiment, the invention provides an exit valve that is configured to open when an actuating pressure is met or exceeded to permit respiratory gases to exit the person""s lungs. An adjustment mechanism is provided to vary the actuating pressure of the exit valve over time, or in a cyclical fashion after one or more chest compressions, with a cycle being a chest compression phase followed by a decompression phase.
In one specific aspect, the actuating pressure of the exit valve is configured to be in the range from about 0 cm H2O to about 20 cm H2O, and more preferably in the range from about 2.5 cm H2O to about 10 cm H2O.
In one particular aspect, the exit valve comprises a valve housing that defines an airway. A valve member is disposed in the housing and is movable between a closed position that prevents the passage of respiratory gases through the airway and an open position where respiratory gases are permitted to flow through the airway. The valve member is configured to remain in the closed position until a pressure acting against the valve member meets or exceeds the actuating pressure. At this point in time, the valve member moves to the open position, allowing expiratory gases to be released.
In one aspect, a biasing mechanism is provided to apply a force against the valve member to bias the valve member in the closed position. With this configuration, the mechanism to vary the actuating pressure may comprise a system to vary the applied force supplied by the biasing mechanism. As one example, the system may comprise a lead screw to move the biasing mechanism over time. In one aspect, the biasing mechanism may comprise a spring. In this way, as the lead screw is turned, the spring is compressed over time, thereby applying a greater force against the valve member. In another aspect, the biasing mechanism may comprise a pair of spaced apart, opposing pole magnets. As the pole magnets are moved closer to each other over time, the force acting against the valve member is increased. Conversely, as the pole magnets are moved further away from each other, the force against the biasing member is lessened.
In another aspect, a knob is provided to manually operate the lead screw. Alternatively, a spring loaded mechanism may be provided to automatically turn the lead screw over time. As another example, the system may comprise a linear actuator to move the biasing member. The linear actuator may be programmed so that it automatically moves the biasing member a predetermined amount over a predetermined time.
In one particular aspect, the housing defines an intake port and the valve member is disposed across the intake port when in the closed position. The housing also defines an exhaust port downstream of the intake port to exhaust respiratory gases once the valve member moves from the closed position. In yet another aspect, the valve member may comprise a float that is disposed within a chamber. With this arrangement, the biasing mechanism may comprise a pressure source to vary the pressure within the chamber.
The exit valve may optionally be included as part of a system for controlling the flow of respiratory gases. For example, the system may also include an impedance valve that is configured to open to permit respiratory gases to flow to the person""s lungs once a threshold negative intrathoracic pressure is met or exceeded. The exit valve may be a valve that is separate from the impedance valve or may conveniently be incorporated into the impedance valve. The system may also include various mechanisms for assisting in a CPR procedure. For example, the system may include a compression mechanism for compressing the person""s chest. A lifting member may also be provided that is adapted to be secured to the person""s chest to actively lift the person""s chest.
In another particular aspect, the system may include an interface member to which the valve is coupled. In this way, the interface member may be coupled to a person""s airway to place the exit valve in communication with the airway. In another alternative, the system may include a compressible bag, with the exit valve being coupled to the compressible bag.